The purpose of this investigation is to examine the role of alpha-Fetoprotein (AFP) in the regulation of estrogen-dependent events during postnatal life in the rat and to elucidate molecular and hormonal mechanisms responsible for the control of AFP. To determine if the postnatal decline in serum AFP is requisite for the appearance of estrogen dependent events during prepubertal and pubertal stages, female rats will receive injections of AFP or its antibody. We predict that AFP will inhibit estrogen dependent processes by binding endogenous estradiol, whereas AFP antibodies should enhance these processes resulting in precocious puberty. These results would provide additional support for the proposal that AFP is an important factor in the regulation of estrogen-dependent events in the rat. Thus, molecular and hormonal factors responsible for the decline in serum AFP potentially represent important steps in the control of reproductive processes in these species. Molecular steps in the regulation of AFP will first be examined to elucidate the basic mechanism responsible for the decline in AFP. The rate of AFP synthesis and degradation as well as the AFP mRNA and gene will be quantitated during development to determine the rate limiting factor in the control of serum AFP. In addition, we will determine whether the postnatal decline in AFP and the molecular mechanism responsible for this decline are influenced by ovarian, thyroid or adrenal hormones. Elucidation of the hormonal factors involved in AFP regulation may provide a better understanding of hormonal interactions in the control of estrogen-dependent processes during postnatal development of the female rat.